This research has two related goals: To understand the ways in which the brain represents space, and to explain clinical visual/spatial disorders in terms of the underlying spatial representations that have been impaired by brain damage. The first goal involves characterizing both the functional architecture of spatial representation in terms of the spatial frames of reference (i.e. coordinate systems) used to code spatial position, the relation between the internal spatial structure of objects and their location in space, and the modality-specificity of spatial representations. The investigator also will attempt to localize the representations so delineated by examination of lesion site in patients who are and are not impaired in a particular form of spatial representation. The second goal is to determine which clinically observable visual-spatial disorders (including hemispatial neglect, constructional apraxia, visual disorientation, closure deficits, visual agnosia, topographic disorientation, and disorders of personal space) are attributable to impaired spatial representation (as opposed to impairments in memory or executive processes, for example), and to begin to characterize the nature of the impairment of spatial representation where such an impairment is implicated.